Basic Concepts Of Drilling
In general, drilling refers to making holes on the surface of the product with drilling tools. Generally speaking, when drilling products on a drilling machine, the drill bit should complete two movements simultaneously:
- The main motion, that is, the rotary motion of the drill bit around the axis (cutting motion);
- Secondary movement is the linear movement of the drill toward the workpiece along the axis (feeding movement).
When drilling, because of the flaws in the drill structure, it will leave traces on the processed parts of the product and affect the processing quality of the workpiece. The machining accuracy is generally below IT10, and the surface roughness is about Ra12.5μm, which belongs to the rough machining category.
Drilling Operation Process
Before drilling, workers need to understand the pattern and use drilling tools to draw the hole’s centerline following the basic requirements of drilling. The centerline must be clear and accurate, and the thinner, the better. Please use a vernier caliper or steel ruler to measure after removing the line on the product surface.
Check Square Or Check Circle
After the workpiece has been marked and passed the inspection, the hole’s centerline should take as the symmetry center. The inspection grid or inspection circle should be drawn as the inspection line for trial drilling so that the drilling direction can be checked and corrected during drilling.
After marking out the corresponding check square or check circle, you should carefully proof the eye. Use drilling tools to make a small spot first, and measure multiple times in different directions of the centerline of the cross to see if the punch is indeed at the intersection of the centerline of the cross, then force the energy to be straight, round, and larger, To accurately center the knife.
Use a rag to clean the machine table, fixture surface, and reference surface of the workpiece, and then clamp the workpiece. The clamping is flat and reliable as required, and it is convenient for inquiry and measurement at any time. It is necessary to pay attention to the workpiece’s clamping method to prevent the workpiece from deforming due to the clamping.
Test drilling must perform before the proper drilling: the chisel edge of the drill bit is aligned with the center of the hole to drill a shallow pit, and then visually check whether the shallow pit is oriented correctly. Continuously correct deviation during the drilling process so that the shallow pit is coaxial with the inspection circle. If the error is small, you can force the workpiece to move in the opposite direction during tripping and gradually correct it.
Machine-added drilling is generally base on manual feed operation. When the test drilling azimuth accuracy is required, the drilling can carry out. When manually feeding, the feed force should not cause the drill bit to bend and avoid the hole axis from skewing.
More Accurate Drilling Methods
Sharpen The Drill
Before drilling, the drill bit must be ground. The sharpened drill bit maintains an accurate apex angle, relief angle, and chisel edge bevel angle. The two leading cutting edges’ length is flat and symmetrical to the centerline of the drill bit. The two main flank surfaces are smooth to facilitate centering and reduce the roughness of the hole wall. The chisel edge and main cutting edge also need to be polished appropriately (it is best to the rough ground on a grinder first, then finish on the oil stone).
Use a height ruler to draw a line accurately. The first thing to do is to ensure that the standard is accurate. When using a height ruler to draw a line accurately, make the angle between the scribing needle and the scribing plane of the workpiece form an angle of 40-60 degrees (along the scribing direction) drawn line is clear and uniform.
After the hole cross line is drawn, use drilling tools to punch out the center point on the cross line (requires a small punch point and correct orientation).
Correctly Clamp The Drilling Tools
Under normal circumstances, the accuracy of holes less than 6mm in diameter is not high, and the workpiece can b clamp with hand pliers for drilling. Gaps of 6-10mm can clamp with flat-nose pliers to keep the workpiece’s surface perpendicular to the spindle of the drilling machine.
When drilling a hole with a larger diameter, the flat-nose pliers must fix with a bolt pressing plate.
Larger workpieces with a hole diameter of more than 10mm can be drilled by clamping by a pressure plate.
After the workpiece clamp, do not rush to drop the drill, and firstly perform an alignment.
The alignment has static alignment and dynamic alignment. The so-called static alignment refers to alignment before the drilling machine is launch so that the centerline of the drilling machine spindle and the cross line of the workpiece are aligned. This method is safe and convenient for beginners, and more comfortable to grasp. Still, because the drilling machine’s swing is not considered, for example, other uncertain factors, the drilling accuracy is low.
The diligent search is carried out during the working process of the drilling machine. While correcting, some uncertain factors can consider, and the drilling accuracy is relatively high.
Detection can accurately and timely find the hole’s accuracy so that necessary measures can be taken to compensate.
For holes with high drilling precision, we generally use drilling, reaming, and reaming processing techniques. After drilling a small hole in the first step, use a caliper to detect the error offset from the bottom hole’s center to the reference plane and calculate the bottom hole’s position and the ideal center through actual measurement.
Suppose the amount of error is not greater than 0.10mm when reaming. In that case, you can adequately increase the drill bit’s top angle, weaken the automatic centering effect, properly push the workpiece in the positive direction, and gradually increase the drill tip’s diameter to compensate.
If the amount of fault is more significant than 0.10mm, you can use assorted round files to trim the two side walls of the bottom hole, and the trimming part should connect with the smooth transition of the bottom hole.
The drilling tools look simple, but how to provide drilling accuracy still requires the operator’s experience and learning.